The frequency for high-speed transmission on a printed board is about to reach a range of 3 to 5 GHz. Differences in the delay time of signals therefore occur between signal lines on a printed board where a plurality of signal lines are laid out on an insulating body in which insulating cloth is disposed. The following describes the differences of delay time. FIG. 6 is a diagram illustrating a printed board made of an insulating material where glass cloth is disposed. FIG. 7 is a diagram illustrating concave and convex portions of glass cloth and signal lines. As illustrated in FIG. 6, a printed board 7 includes an insulating body 71 that is glass cloth 711, which serves as insulating cloth, impregnated with resin; and printed wiring 72 including a plurality of signal lines that run parallel to each other. The glass cloth 711 is woven from glass fibers that cross each other at right angles. As illustrated in FIG. 7, on the printed board 7, a plurality of signal lines in the printed wiring 72 are located differently relative to the concave and convex portions of the glass fibers depending on where the signal lines are disposed. Much of the printed wiring 72 is parallel or at right angles to the glass fibers, in which case the position of each signal line in the printed wiring 72 relative to the concave and convex portions of the glass fibers is always constant. Since there is a difference in permittivity between the glass fibers and the resin, the distance from the glass fibers causes the differences in the delay time of signals between the signal lines.
A technique of laying out signal lines in a zigzag pattern is known to dissolve the differences of delay time. FIG. 8 is a diagram illustrating signal lines laid out in a zigzag pattern. As illustrated in FIG. 8, on a printed board 8, printed wiring 82 is laid out in a zigzag pattern so as not to be parallel or at right angles to the glass fibers of the insulating body 71. Thus, the distances between each of a plurality of signal lines in the printed wiring 82 and the glass fibers are never fixed. Therefore, it is possible to reduce the differences in the delay time of signals between the signal lines. However, the zigzag pattern makes the lines longer than the normal way of wiring, making it impossible to propagate high-speed signals in a stable manner in the range of 5 to 10 GHz. Moreover, the zigzag pattern leads to deterioration of signal waveforms, reductions in the density of wiring, increasing transmission loss and the like due to the longer lines.
A technique of providing the printed wiring tilted at 45 degrees to an insulating body is known to solve the above problem. FIG. 9 is a diagram illustrating a printed board whose printed wiring is tilted at 45 degrees to an insulating body. As illustrated in FIG. 9, on a printed board 9, printed wiring 91 as a whole is tilted at 45 degrees to the insulating body 71 in order to obtain the same effect as the zigzag pattern does without changing the routes of a plurality of signal lines 911. Therefore, the differences of delay time between the signal lines 911 decrease without leading to deterioration of signal waveforms, reductions in the density of wiring, increased transmission losses and the like.
Patent Document 1: Japanese Laid-open Patent Publication No. 2008-193073
Patent Document 2: Japanese Laid-open UM Publication No. 05-15467
However, as illustrated in FIG. 9, the 45-degree tilting of the printed wiring 91 on the insulating body 71 requires a larger insulating body 71 compared with the one that is not tilted, resulting in a significant decrease in the efficiency of cutting the board.